1. Field of the Invention
This invention relates to a lithographic printing plate precursor and a method for preparing a lithographic printing plate using the same.
2. Description of the Related Art
In general, a lithographic printing plate has a surface consisting of an oleophilic image area and a hydrophilic non-image area. Lithographic printing means a printing method that comprises alternately supplying a fountain solution and an oily ink on the surface of lithographic printing plate, making the hydrophilic non-image area a fountain solution-receptive area (an ink unreceptive area), allowing the oleophilic image area alone to receive the ink by utilizing the nature of the fountain solution and the oily ink to repel with each other, and then transferring the ink to a printing material such as paper.
To prepare the lithographic printing plate, there has been widely employed a lithographic printing plate precursor (a PS plate) comprising a hydrophilic support and an oleophilic image forming layer (hereinafter also called “a photosensitive layer”). Ordinarily, a lithographic printing plate is obtained by a plate making process which comprises exposing the lithographic printing plate precursor through an original such as a lith film, and, while leaving the image forming layer serving as the image areas removing the image forming layer in the unnecessary non-image area by dissolving in an alkaline developing solution or an organic solvent thereby exposing the surface of the hydrophilic support to form the non-image area.
In the existing plate-making process of lithographic printing plate precursor, it is required to employ after the exposure the step of removing the unnecessary image forming layer by dissolving in a developing solution or the like. Thus, it is one of the problems to be solved to simplify such an additional wet treatment described above. As one simplification means, it is desirable if the development can be carried out with a nearly neutral aqueous solution or simply with water.
With the recent spread of digitalized technique of electronically processing, accumulating and outputting image information using a computer, on the other hand, various new image outputting systems fitting for the digitalized technique have been put into practical use. Accordingly, attention has been drawn to a computer-to-plate technique wherein digitalized image information is carried on highly converging radiation such as laser beams and a lithographic printing plate precursor is scan-exposed with the light thereby directly preparing a lithographic printing plate without resorting to a lith film. Thus, it is one of the important technical problems to obtain a lithographic printing plate precursor appropriate for the technique described above.
Under these circumstances, it has been urgently required more than before to provide a plate making operation that is appropriate for both simplification and digitalization.
To meet the above-described requirement, for instance, JP-A-2002-365789 discloses that by incorporating a compound having an ethylene oxide chain into an image forming layer of a lithographic printing plate precursor comprising a hydrophilic support and the image forming layer containing a hydrophobic precursor, a hydrophilic resin and a light-to-heat converting agent, the lithographic printing plate precursor becomes usable not only in on-press development but also in printing following exposure and wet development processing with the use of water or an appropriate aqueous solution as a developing solution.
Further, US 2004/0013968 discloses a processing method of lithographic printing plate precursor which comprises preparing a lithographic printing plate precursor comprising (i) a hydrophilic support and (ii) an oleophilic heat-sensitive layer which contains a radical-polymerizable ethylenically unsaturated monomer, a radical polymerization initiator and an infrared absorbing dye, is hardened with infrared laser exposure and is developable with an aqueous developing solution containing 60% by mass or more of water and having pH of 2.0 to 10.0, exposing imagewise the lithographic printing plate precursor with an infrared laser, and removing the unhardened area of the heat-sensitive layer with the aqueous developing solution.